The present invention relates to sealing devices. In particular, although not exclusively, the invention relates to a gland wherein fluid pressure is applied to energise the follower. The invention also relates to repair and replacement of conventional sealing devices.
A conventional shaft sealing arrangement is illustrated in FIG. 1 and indicated by numeral 10. The shaft sealing arrangement 10 is arranged to provide a fluid seal around the shaft 11 where the shaft 11 exists the machine housing through a portion of the machine housing 12. The portion 12 defines an annular recess adjacent the shaft 11 in which packing 14 is provided. A gland follower 16 operates to compress the packing 14 within the recess. As the packing 14 is compressed axially ie parallel to the axis of the shaft 11, the packing 14 applies a radial force to the shaft 11, thereby sealing against the shaft. The gland follower 16 is secured to the portion 12 of the machine housing by bolts 18 and nuts 20. The nuts and bolts 18, 20 can also control the compressive force applied by the gland follower 16 to the packing 14. As shown, the shaft sealing arrangement 10 is conventionally assembled between the portion 12 of the machine housing and the bearing 13. The bearing 13 is retained in place by bearing bracket 15 secured by fasteners 17.
A disadvantage of this arrangement is that as the packing 14 wears the compressive force applied to the packing 14 will decrease. Therefore, regular maintenance checks are required. This may involve regular tightening of the nuts 20. The labour involved in maintaining conventional sealing arrangements 10 in operating order is therefore high.
The illustrated arrangement in FIG. 1 shows considerable space between the machine housing 12 and the bearing 13. This is not always the case and where the portion 12 is closely spaced to the bearing 13, difficulties will be encountered in accessing and tightening nuts 20. Further difficulties will also be encountered in repacking the packing 14 as required.
It is therefore an object of the present invention to provide a sealing device which overcomes or at least ameliorates some of the above mentioned disadvantages. Additionally, it is an aim of a preferred embodiment of the present invention to replace of the present invention is at least to provide the public with a useful choice.
In accordance with a first aspect of the invention, there is provided a sealing device for sealing about a rotatable member extending through a machine housing, the sealing device including: primary sealing means disposed in a recess of the machine housing for sealing against the rotatable member; a follower for compressing the primary sealing means; a follower housing connected to the machine housing and of annular form for mounting about the rotatable member with an axial direction of the follower housing aligned with the rotational axis of the rotatable member, wherein the follower housing includes inner and outer annular walls, with the follower having an annular body portion which is slidingly engageable with both the inner and outer annular walls, an annular chamber being defined by the inner and outer annular walls and a pressure face of the follower, the chamber having means to receive fluid; the follower being slidable within the follower housing generally in the axial direction and having sliding interfaces for interfacing with the inner and outer walls of the follower housing, there being further provided, secondary sealing means at the sliding interfaces for sealing against the egress of fluid from the chamber along the sliding interfaces of the follower.
The sealing device defined above may be used in any application where a conventional sealing device is used eg. pumps, augers, valves.
The primary sealing means may be in the form of packing conventionally used in sealing devices although other sealing means such as elastomeric rings are considered within the scope of the present invention.
Preferably the follower is in the form of an annular piston received within the follower housing. In a preferred form of the invention, the piston further includes an annular extension extending beyond the follower housing and into the recess in the machine housing. The follower may come in two or more parts such as two symmetrical halves to aid assembly.
The follower housing may come in two or more parts such as two symmetrical halves to aid assembly.
The secondary sealing means may be of any form although conventional piston rings are the preferred form.
The sealing device may be adapted to utilise any fluid such as air or hydraulic fluid for energising the follower. When the sealing device is used in applications transferring a clean liquid eg. water, oil or stream, a connection may be provided from the discharge of the transferring apparatus to the sealing device. In other applications, an independent fluid supply may be adopted. This might include a source of compressed air or a hydraulic system could be employed.
Additionally, control means may be provided to control the fluid pressure. Preferably the control means provides a constant fluid pressure to the chamber. Thus if the chamber starts to leak, further fluid will be provided to maintain the pressure and the sealing device remains in operation. The control system may be adapted to provide an alarm condition when the amount of further fluid reaches an unacceptable level. The control system may comprise a P.L.C. with feedback. Alternatively, an air cylinder with a regulator may be appropriate.
In another preferred form of the invention, the follower may comprise two parts, a first packing portion and a second piston portion. The first packing portion maybe in the form of an annular body portion with an annular extension. The second piston portion may be in the form of an annular piston. The two portions may be held in spaced configuration by a biasing means urging the two portions apart, such as a spring. Moreover, instead of an open fluid system whereby the chamber is supplied with fluid to a predetermined pressure, the fluid system may be essentially closed. For example, the follower housing may define a forward chamber between the first follower portion and the forward wall of the housing and a rear chamber between the second piston portion and the rear wall of the follower housing. The forward and rear chambers are interconnected for fluid flow therebetween. Furthermore, the pressure face of the first follower portion against which the fluid acts in use may be smaller than the pressure face of the second portion to maintain a greater force against the second portion than the first portion, this difference being balanced by the reaction force acting against the first follower by the packing. As the packing wears with a consequent reduction in the reaction force applied to the first follower portion, the greater force on the second follower portion urges both follower portions forwardly, with the force being transmitted through the spring to the first follower portion. This brings about a consequent reduction in the volume of the forward chamber. With the first and second chambers fluid-filled in use, a reduction in the volume of the forward chamber will cause fluid to flow to the second chamber. As the area of the pressure face of the second follower portion is greater than the first, the second follower portion will not move the same distance as the first follower portion. The spring thus takes up the slack between the two follower portions.
It will be appreciated that the various parts are unlikely to move in step-wise fashion as explained above. Rather, it is expected that the various parts of the device move gradually to retain equilibrium of the various forces acting on the various parts.
In accordance with a second aspect of the present invention, there is provided a kit for sealing about a rotatable member extending through a machine housing, the kit including: a follower for compressing packing which is disposed within a recess of the machine housing against the rotatable member; a follower housing connectable to the machine housing and of annular form for mounting about the rotatable member with an axial direction of the follower housing aligned with the rotational axis of the rotatable member, wherein the follower housing includes inner and outer annular walls, with the follower having an annular body portion which is slidingly engageable with both the inner and outer annular walls, an annular chamber being defined by the inner and outer annular walls and a pressure face of the follower, the chamber having means to receive fluid; the follower being slidable within the follower housing generally in the axial direction and having sliding interfaces for interfacing with the inner and outer walls of the follower housing, there being further provided, secondary sealing means at the sliding interfaces for sealing against the egress of fluid from the chamber along the sliding interfaces of the follower.
The preferred features recited above in connection with the first aspect of the invention may also have application in respect of the second aspect of the invention, including the feature of the two part follower.
The kit may be retro-fitted onto a rotatable member with a conventional sealing device. In so doing, the packing may be repacked. Preferably, the installation is achieved by removing the existing gland follower and nut of the conventional sealing device and replacing this with the kit as defined. The follower housing may be attached to the machine housing to which the gland follower was previously attached. This may be achieved by providing a portion of the follower housing as an attachment plate which is initially attached to the machine housing. The remaining portion of the follower housing is connectable to the attachment plate with the follower positioned to act against the packing.
In certain applications, there may be insufficient clearance between the machine housing and an adjacent bearing bracket to insert the follower housing and follower. In such cases, the kit may be installed by attaching the follower housing to the bearing bracket. An adaptor means may be provided for this purpose.
The secondary sealing means may be in any form although conventional piston rings are the most preferred.
The kit may also include means for applying fluid to the chamber.
In accordance with a third aspect of the present invention, there is provided a method of upgrading a conventional sealing device for a rotatable member extending through a machine housing where the conventional sealing device includes a gland follower attached to the machine housing and packing disposed in a recess of the machine housing against the rotatable member, the method including: removing the gland follower of the conventional sealing device; and installing a kit comprised of a follower and follower housing by attaching the follower housing to the machine housing, with the follower positioned to act against the packing, wherein the follower housing is of annular form for mounting about the rotatable member with an axial direction of the follower housing aligned with the rotational axis of the rotatable member, wherein the follower housing includes inner and outer annular walls, with the follower having an annular body portion which is slidingly engageable with the inner and outer annular walls, an annular chamber being defined by the inner and outer annular walls and a pressure face of the follower, the chamber having means to receive fluid, the follower being slidable within the follower housing generally in the axial direction and having sliding interfaces for interfacing with the inner and outer walls of the follower housing, there being further provided, secondary sealing means at the sliding interfaces for sealing against the egress of fluid from the chamber along the sliding interfaces of the follower.
Preferably the follower housing is installed by the use of an attachment plate forming part of the follower housing. The attachment plate may be connected in place of the existing gland follower(s). Optionally the same fastening means may be used. The remaining part of the housing may then be secured to the attachment plate. A threaded connection between the remaining part of the housing and the attachment plate may be provided for this purpose.
It will be appreciated that the use of the follower housing may take up additional space when compared with the existing sealing arrangement. In some applications therefore, there may be insufficient room between the machine housing and the bearing bracket for the replacement follower and follower housing to be installed given the required configuration of the replacement follower. In such applications, the follower housing may be secured to the bearing bracket by the use of an adaptor means.
In accordance with a fourth aspect of the present invention, there is provided a method of upgrading a conventional sealing device for a rotatable member extending through a machine housing where the conventional sealing device includes a gland follower attached to the machine housing and packing disposed in a recess of the machine housing against the rotatable member, with a bearing bracket positioned adjacent the machine housing, the method including; removing the gland follower of the conventional sealing device; and installing a kit comprised of a follower and follower housing by attaching the follower housing to the bearing bracket, with the follower positioned to act against the packing, wherein the follower housing is of annular form for mounting about the rotatable member with an axial direction of the follower housing aligned with the rotational axis of the rotatable member, wherein the follower housing includes inner and outer annular walls, with the follower having an annular body portion which is slidingly engageable with the inner and outer annular walls, an annular chamber being defined by the inner and outer annular walls and a pressure face of the follower, the chamber having means to receive fluid, the follower being slidable within the follower housing generally in the axial direction and having sliding interfaces for interfacing with the inner and outer walls of the follower housing, there being further provided, secondary sealing means at the sliding interfaces for sealing against the egress of fluid from the chamber along the sliding interfaces of the follower.
Either of the above methods may additionally include repacking the packing.
The replacement follower may take any of the forms described above in connection with the first aspect of the invention including the two part form.
This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.
The invention consists in the foregoing and also envisages constructions of which the following gives examples only.